1. Field of the Invention
The present invention relates to what is called a FIMS (Front-opening Interface Mechanical Standard) system that is used in a semiconductor manufacturing process or the like to transfer wafers stored in the interior of a transfer container called a pod from one semiconductor processing apparatus to another. More specifically, the present invention relates to a FIMS system or a lid opening and closing system in which a closed container for storing wafers in the form of a pod called FOUP (Front-Opening Unified Pod) is placed thereon, the lid of the pod is opened and closed to bring wafers into it, and a purge mechanism that cleans the interior of the pod is provided.
2. Related Background Art
In the past, the semiconductor manufacturing process had been performed in what is called a clean room that is constructed by establishing a high degree of cleanliness in the room in which semiconductor wafers are handled. In recent years, however, in view of an increase in the wafer size and with a view to reduce cost incurred in maintenance of the clean room, use has been made of a method of keeping clean only the interior of a processing apparatus, a pod (or wafer container) and a mini-environment through which substrates or wafers are transferred between the pod and the processing apparatus.
The pod is composed of a substantially cubical body having shelves provided therein that can hold a plurality of wafers in a parallel and separated state and an opening provided on one side thereof through which wafers can be brought into/out of it, and a lid for closing the opening. Those pods which have an opening portion provided not on the bottom but on one lateral side thereof (i.e. the front side to be opposed to the mini-environment) are collectively called FOUP (Front-Opening Unified Pod). The present invention mainly pertains to technologies in which the FOUP is used.
A structure that defines the above mentioned mini-environment has a first opening portion to be opposed to the opening of the pod, a door that closes the first opening portion, a processing apparatus side opening portion provided on the semiconductor processing apparatus side of the unit, and a transferring robot that is adapted to reach into the interior of the pod through the first opening portion to pick up a wafer and transfer the wafer into the processing apparatus through the processing apparatus side opening portion. The structure that defines the mini-environment also has a support table that supports the pod in such a way that the pod opening is placed just in front of the door.
On the top surface of the support table are provided positioning pins to be fitted into positioning holes provided on the bottom surface of the pod to regulate the placement position of the pod and a clamp unit for engaging with a clamped portion provided on the bottom surface of the pod to fix the pod to the support table. Typically, the support table is adapted to be movable toward and away from the door over a predetermined distance. When the wafers in a pod are to be transferred into the processing apparatus, the pod placed on the support table is moved until the lid of the pod abuts the door, and then after abutment, the lid is removed by the door. By this process, the interior of the pod and the interior of the processing apparatus are bought into communication with each other through the mini-environment to allow wafer transferring operations that will be performed repeatedly. All of the support table, the door, the first opening portion, a mechanism for opening and closing the door and a wall partly defining the mini-environment and having the first opening are included in the FIMS (Front-opening Interface Mechanical Standard) system.
Normally, the interior of the pod in which wafers or the like are stored is filled with dry nitrogen gas that is maintained highly clean to prevent contaminative materials and oxidizing gas etc. from entering the interior of the pod. However, when the wafers in the pod are brought into a processing apparatus to perform a specific processing thereon, the interior of the pod and the interior of the processing apparatus are continuously kept in communication with each other. A fan and a filter are provided in the upper portion of the chamber in which the transfer robot is disposed, so that particle-controlled clean air is normally introduced into the chamber. However, if such air enters the interior of the pod, there is a possibility that the surface of the wafers is oxidized by oxygen or moisture contained in the air.
In association with miniaturization and higher performance of semiconductor elements, oxidization caused by oxygen etc. entering the interior of the pod is recently being paid attention to, though it was not a serious problem before. Such oxidizing gases may generate ultra-thin oxide film on the surface of a wafer or on various layers formed on a wafer. Due to the presence of such an oxide film, there is a possibility that desired characteristics of miniaturized elements are not ensured. A countermeasure to this is to prevent gases in which the oxygen partial pressure is not controlled from entering the interior of the pod from the exterior of it. As a specific method, Japanese Patent Application Laid-Open No. 11-145245 teaches to provide a gas supply nozzle and a suction nozzle in the region adjacent to the opening of the pod in a FIMS system to form an air curtain that substantially closes the pod opening. The air curtain thus formed prevents external gases from entering the interior of the pod.
In the interior of semiconductor manufacturing apparatuses, a gas with which various wiring etc. formed on a wafer can be contaminated is sometimes used in a process such as etching in the interior of the processing apparatus. Japanese Patent Application Laid-Open No. 2003-007799 discloses a method for preventing such contaminant gases from entering the interior of the pod from the interior of the processing apparatus in such cases. In this method also, a fan is used to form an air curtain in front of the opening of the pod in a FIMS system so as to prevent gases from flowing into the interior of the pod from the processing apparatus. This method is considered to be effective in preventing oxygen from flowing into the interior of the pod.
However, when these methods were implemented practically, it was found that the oxygen partial pressure in the interior of the pod significantly increased in fact just after the pod opening is opened. In view of this, these methods need to be further improved to meet the aforementioned demand. Given the above described situation, the inventor of the present invention previously developed a system in which entrance of oxidizing gases into the interior of the pod is prevented by changing the shape of the gas supply nozzle used in forming the air curtain in various ways and reducing the oxygen concentration in the gas that forms the air curtain also at positions distant form the nozzle. Furthermore, the inventor previously developed a system in which a purge gas is introduced into the interior of the pod in addition to forming an air curtain to further reduce oxidizing gases in the interior of the pod. However, to meet various demands such as higher performance of semiconductor devices or increases in the processing performance of semiconductor manufacturing apparatuses, a further reduction in the partial pressure of oxidizing gases in the pod mounted on the FIMS system is desired.